Oi Goemon's name derives from green tea brands Oi Ocha and Iemon. In the original series, this recent arrival to the area acts as an ally. He adopts an older brother role toward protagonist Cota Coga, offering advice delivered in a distinctive kabuki tone. His specialty is sniping competitions using his control-type Bottleman, Gyokurock. He sports curly dark green and brown hair with a light green fade, conveying a relaxed demeanor, and wears a green and white jacket over a black shirt, baggy purple shorts, and flip-flops.

In the DX storyline, his role shifts to rival. He holds the title of #1 Battle Star. After Team Citrus wins a three-game match, he joins them out of responsibility as a top-ranked battler, becoming one of its commanding members. Unlike other Team Citrus members, he appears unaffected by Reburst's manipulation, freely expressing emotions and remaining skeptical of AI Citrus's new Bottle Battle system. His DX appearance features dark green hair with orange tints, an orange eye visible while his left eye is covered by a black eyepatch. His attire consists of a green jacket, a green and orange T-shirt, purple shorts, sandals, and a green clip necklace.

Across both series, his personality consistently incorporates dramatic flair and kabuki-inspired mannerisms. His Bottleman remains the control-type Gyokurock. A notable distinction in DX is his exclusive use of a Prototype System Bottleman instead of the common Drink Cross System.